Psychology's Second Most Misunderstood Concept?

My nominee for psychology’s most misunderstood concept is negative reinforcement (which is not punishment, but actually a rewarding event—withdrawing or reducing something aversive, as when taking aspirin is followed by the alleviation of a headache).

In second place on my list of oft-misunderstood concepts is heritability.

My publishers’ twitter feed today offered this:

Sure enough, the news source says it’s so. But it isn’t. Tracking back to the actual study, and its own press release, we see that, as we might have expected, the conclusion was drawn from a twin study that estimated the genetic contribution to variation among individuals in autism spectrum disorder (ASD) scores.

Heritability refers to the extent to which differences among people are due to genes. If the heritability of ASD is 80 percent, this does not mean that 80 percent of autism cases are attributable to genes and 20 percent of cases to environment. And it does not mean that any particular case is 80 percent attributable to genes and 20 percent to environment. Rather it means that, in the context studied, 80 percent of the differences among people was attributable to genetic influence.